How Many Bags of Concrete for a 4x8 Slab?
Small pads like a 4x8 suit bagged mix. How many bags of concrete for a 4x8 slab at a standard 4-inch depth: 18 × 80 lb, or 24 × 60 lb, since each bag yields only about 0.6 or 0.45 cubic feet.
Concrete calculator →How the bag count is figured
- Area: 4 × 8 = 32 sq ft.
- Volume at 4 in: 32 × 0.333 = 10.67 cu ft.
- 80 lb bags: 10.67 ÷ 0.60 = 17.8, round up to 18.
- 60 lb bags: 10.67 ÷ 0.45 = 23.7, round up to 24.
Check the yield printed on your brand’s bag, since it varies a little. The concrete calculator handles other shapes.
Related: How Many Bags of Concrete for a 10x10 Slab?
Bags by thickness for a 4x8 slab
| Thickness | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3 in | 8.00 | 14 | 18 | 27 |
| 4 in | 10.67 | 18 | 24 | 36 |
| 5 in | 13.33 | 23 | 30 | 45 |
| 6 in | 16.00 | 27 | 36 | 54 |
Is bagged mix the right call?
At 0.40 cubic yards, this pad is well under the point where a ready-mix truck starts to make sense. Many plants charge a small-load fee on tiny orders, so bags are often cheaper here, and a rented mixer makes 18 bags manageable for two people.
Related: How Many Bags of Concrete for an 8x10 Slab?
Forms and base
A small slab still needs a firm base. Compact the soil, add compacted gravel and set forms to the finished height. If the pad will hold an AC unit, a generator or a grill, keep the top a little above the surrounding grade so water does not pool against it. Mixing 18 bags takes time, so stage them next to the forms before you start.
Buying the bags
A pallet of 80 lb bags often holds around 40 to 42 bags, so this job is about 1 pallet or less. Buy one or two extra bags: returning an unopened bag is easier than running out mid-pour.
Questions people ask
How many 80 lb bags for a 4x8 slab?
About 18 bags at 4 inches thick.
How many 60 lb bags for a 4x8 slab?
About 24 bags at 4 inches thick.
How many bags for a 4x8 slab 6 inches thick?
About 27 bags of 80 lb mix or 36 of 60 lb.
How much does an 80 lb bag of concrete yield?
About 0.6 cubic feet of mixed concrete.
How thick should the base under the slab be?
About 4 inches of compacted gravel is common for residential slabs, more on soft or poorly drained soil.
Related guides
- How Much Area Does a Yard of Concrete Cover?
- How Many Bags of Concrete in a Yard? 40, 60, 80 lb
- Gravel Base Under a Concrete Slab: Depth and Tons
- How Many Yards in a Concrete Truck? Mixer Sizes
- Concrete Short Load Fee: What It Is and How to Cut It
- 60 lb vs 80 lb Concrete Bags: Yield, Count, and Cost
- Rebar vs Wire Mesh in a Slab: Which One to Use
- How Many Bags of Concrete for a 4x5 Slab?
- How Many Bags of Concrete for a 5x8 Slab?
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